Power brake systems for vehicles[d1], for example, including hybrid electric vehicles (HEV's), typically include a hydraulic brake boosting system which increases the hydraulic force applied to the brakes when engaging a vehicle brake system (e.g., depressing a brake pedal).
A hydraulic brake system typically includes a vacuum pump which may be operated by a motor connected to the vehicle power system so as to generate negative pressure (vacuum) on a working fluid (e.g., air) which is stored in a brake booster, e.g., attached to the master cylinder Typically, when the brake pedal is engaged (e.g., depressed), negative pressure is introduced into the hydraulic brake system to increase (boost) the force applied to the brake system (e.g., master cylinder) in order to operate the brakes.
In order to assure that there is enough accumulated pressure to operate the brake system, various strategies in the prior art have been proposed for operating the vacuum pump.
Ishi (U.S. Pat. No. 6,135,577) discloses a “pump operation control apparatus for hydraulic brake boosting system” that determines whether an ignition switch has been switched on and a first timer measures the time in response to an ON signal of the ignition switch. When the time measured by the first time is longer that a predetermined time interval, the pump is operated.
Ichikawa (USPUB 2006/158028) discloses a “control system for brake vacuum pump” where a control unit determines when a vehicle has a speed equal to or greater than a preset creep speed after the startup of the engine, at which time the control unit allows operation of the vacuum pump.
Wada et al. (JP2020465) discloses a “control device for vacuum pump motor for vehicle” to reduce noise generation and power consumption by turning on a vacuum pump motor power source when an engine is started.
Tanihata (JP80983118) discloses “control method of hybrid electric vehicle” where operation of the brake booster vacuum pump and the power steering pump is prohibited until the engine that drives them is started and where the revolution rate of the engine is sensed to determine whether the engine is started.
Further methods are desirable for controlling the operation of a vacuum pump included in a hydraulic brake system (brake booster vacuum pump) in order to reduce power consumption and reduce pump operating noise, thereby improving brake booster vacuum pump operation.
Thus, there is a need for improved methods to control the operation of a vacuum pump included in a hydraulic brake system (brake booster vacuum pump) in order to improve operating efficiency of the brake system including reduced power consumption and reduced pump operating noise.
Therefore it is an object of the invention to provide an improved method to control the operation of a vacuum pump included in a hydraulic brake system (brake booster vacuum pump) in order to improve operating efficiency of the brake system including reduced power consumption and reduced pump operating noise.